Prepare your Active Directory environment

Before you can begin to upgrade the first Windows Server 2003 Domain Controller to a Windows Server 2008 Domain Controller, you first have to prepare the Active Directory.
Microsoft provides a tool called adprep.exe to facilitate this preparation. You need to run the following commands on the following servers in your Active Directory environment:
You need to run the following commands on the following servers in your Active Directory environment:

Command	Domain Controller
adprep.exe /forestprep	Schema Master
adprep.exe /domainprep	Infrastructure Master
adprep.exe /domainprep /gpprep	Infrastructure Master
adprep.exe /rodcprep *	Domain Naming Master

                               * Optional when you want to deploy Read Only Domain Controllers.
After preparing your Active Directory for Windows Server 2008 be sure to check the process. Breadcrumbs to failures may be found in the event viewer, but real men will check the adprep.log files.
Allow sufficient time for proper replication to all your Windows Server 2003 Domain Controllers. (In large environments with specific replication needs this might take hours.) When you feel all changes have been replicated use the replmon and repadmin tools to check and optionally troubleshoot Active Directory replication.